U.S. patent number 8,630,780 [Application Number 12/990,828] was granted by the patent office on 2014-01-14 for brake system and method for operating a brake system.
This patent grant is currently assigned to Robert Bosch GmbH. The grantee listed for this patent is Konstantin Agapov, Michael Bunk, Andreas Krautter, Matthias Schanzenbach. Invention is credited to Konstantin Agapov, Michael Bunk, Andreas Krautter, Matthias Schanzenbach.
United States Patent |
8,630,780 |
Bunk , et al. |
January 14, 2014 |
**Please see images for:
( Certificate of Correction ) ** |
Brake system and method for operating a brake system
Abstract
A method for controlling a brake system including receiving a
braking signal for setting a braking action by the brake system,
ascertaining a minimum rate of pressure increase in the brake
system in order to effect the braking action within a predefined
response time, and setting a pumping capacity of a pump of the
brake system so that the pressure in the brake system increases in
accordance with the minimum rate.
Inventors: |
Bunk; Michael (Hampton VIC,
AU), Agapov; Konstantin (Abstatt, DE),
Krautter; Andreas (Steinheim, DE), Schanzenbach;
Matthias (Eberstadt, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Bunk; Michael
Agapov; Konstantin
Krautter; Andreas
Schanzenbach; Matthias |
Hampton VIC
Abstatt
Steinheim
Eberstadt |
N/A
N/A
N/A
N/A |
AU
DE
DE
DE |
|
|
Assignee: |
Robert Bosch GmbH (Stuttgart,
DE)
|
Family
ID: |
41212412 |
Appl.
No.: |
12/990,828 |
Filed: |
December 17, 2008 |
PCT
Filed: |
December 17, 2008 |
PCT No.: |
PCT/EP2008/067756 |
371(c)(1),(2),(4) Date: |
February 28, 2011 |
PCT
Pub. No.: |
WO2009/141023 |
PCT
Pub. Date: |
November 26, 2009 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
|
US 20110166762 A1 |
Jul 7, 2011 |
|
Foreign Application Priority Data
|
|
|
|
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May 20, 2008 [DE] |
|
|
10 2008 001 868 |
Jun 24, 2008 [DE] |
|
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10 2008 002 596 |
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Current U.S.
Class: |
701/70;
303/10 |
Current CPC
Class: |
B60T
8/1755 (20130101); B60T 8/4059 (20130101); B60T
8/4872 (20130101); B60T 2270/308 (20130101); B60T
2201/12 (20130101) |
Current International
Class: |
G06F
7/70 (20060101) |
Field of
Search: |
;701/78,70
;303/3,10,15,155 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1972831 |
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May 2007 |
|
CN |
|
196 32 311 |
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Feb 1998 |
|
DE |
|
197 12 889 |
|
Oct 1998 |
|
DE |
|
198 28 553 |
|
Feb 2000 |
|
DE |
|
8-127331 |
|
May 1996 |
|
JP |
|
2000-79873 |
|
Mar 2000 |
|
JP |
|
2000-203401 |
|
Jul 2000 |
|
JP |
|
2005-59625 |
|
Mar 2005 |
|
JP |
|
2007-216774 |
|
Aug 2007 |
|
JP |
|
2008-18775 |
|
Jan 2008 |
|
JP |
|
Other References
International Search Report, PCT International Patent Application
No. PCT/EP2008/067756, dated Apr. 8, 2009. cited by
applicant.
|
Primary Examiner: Tran; Khoi
Assistant Examiner: Huynh; Luke
Attorney, Agent or Firm: Kenyon & Kenyon LLP
Claims
What is claimed is:
1. A method for controlling a brake system, comprising: receiving a
braking signal for setting a braking action by the brake system;
ascertaining a minimum rate of pressure increase in the brake
system in order to effect the braking action within a predefined
response time; and setting a pumping capacity of a pump of the
brake system so that the pressure in the brake system increases in
accordance with the minimum rate, wherein the pumping capacity is
set as a function of the minimum rate of pressure increase.
2. The method as recited in claim 1, wherein the braking signal
predefines the response time for the braking action.
3. The method as recited in claim 1, wherein the pumping capacity
is a linear function of the minimum rate of pressure increase.
4. The method as recited in claim 1, wherein the braking signal
predefines a setpoint pressure, a switchover valve is set to the
predefined setpoint pressure, and the pumping capacity is set by
the switchover valve as a function of a predefined flow when the
predefined setpoint pressure is reached.
5. A method for controlling a brake system, comprising: receiving a
braking signal for setting a braking action by the brake system;
ascertaining a minimum rate of pressure increase in the brake
system in order to effect the braking action within a predefined
response time; and setting a pumping capacity of a pump of the
brake system so that the pressure in the brake system increases in
accordance with the minimum rate, wherein an instantaneous dead
volume of the brake system is determined and the pumping capacity
is determined as a function of a current dead volume.
6. The method as recited in claim 5, wherein the braking signal
predefines the response time for the braking action, and the
pumping capacity is set as a function of a quotient of the
instantaneous dead volume and the response time.
7. The method as recited in claim 5, wherein the instantaneous dead
volume of the brake system is read from a data memory of the brake
system.
8. A method for controlling a brake system, comprising: receiving a
braking signal for setting a braking action by the brake system;
ascertaining a minimum rate of pressure increase in the brake
system in order to effect the braking action within a predefined
response time; and setting a pumping capacity of a pump of the
brake system so that the pressure in the brake system increases in
accordance with the minimum rate, wherein at least one of a
transverse acceleration and a velocity is detected, and the pumping
capacity is increased when the at least one of the transverse
acceleration and velocity increases.
9. A method for controlling a brake system, comprising: receiving a
braking signal for setting a braking action by the brake system;
ascertaining a minimum rate of pressure increase in the brake
system in order to effect the braking action within a predefined
response time; and setting a pumping capacity of a pump of the
brake system so that the pressure in the brake system increases in
accordance with the minimum rate, wherein the braking signal
predefines a setpoint pressure, an instantaneous actual pressure in
the brake system is determined, based on a characteristic of the
brake system a volume of brake fluid is ascertained which will
raise the pressure from an actual pressure to the setpoint pressure
when pumped into the brake system, and the pumping capacity of the
pump is set as a function of the volume ascertained and the
predefined response time.
10. A brake system having: a pump to build up a hydraulic pressure
in a line to which at least one brake element is connected; and a
control system to set a pumping capacity of the pump, the control
system adapted to receive a brake signal for setting a braking
action by the brake system, ascertain a minimum rate of pressure
increase in the brake system in order to effect the braking action
within a predefined response time, and set a pumping capacity of
the pump so that the pressure in the brake system increases in
accordance with the minimum rate, wherein the pumping capacity is
set by the control system as a function of the minimum rate of
pressure increase.
Description
FIELD OF THE INVENTION
The present invention relates to a brake system and a method for
operating a brake system.
BACKGROUND INFORMATION
In brake systems for motor vehicles, pumps are employed to enable
active braking. The pumps are designed in such a way that they are
able to pump sufficient brake fluid into the brake lines for any
requested braking action in a predefined time period. One minimum
demand comes from driver assistance or vehicle dynamics control
systems, which initiate full braking or brief, individual braking
of individual wheels to stabilize the vehicle in borderline
situations. In this case a large volume of brake fluid must be
pumped in a short time, so that a high rotational speed of the
pumps is necessary.
However, high pump speed results in unacceptable noise
generation.
During calibration, a rotational speed for the brake system is
defined which represents a compromise between braking dynamics and
noise generation. The compromise is determined on the basis of
prior driving trials and empirical values from comparable brake
systems. This results in considerable effort to find the
compromise, as well as the risk of underestimating the requisite
rotational speeds.
SUMMARY
An example method according to the present invention for
controlling a brake system includes receiving a braking signal for
setting a braking action by the brake system; ascertaining a
minimum rate of pressure increase in the brake system in order to
effect the braking action within a predefined response time; and
setting a pumping capacity of a pump of the brake system so that
the pressure in the brake system increases in accordance with the
minimum rate.
The pumping capacity of the pump, for example the return pump, is
adjusted to a currently requisite delivery requirement for brake
fluid. The delivery requirement is estimated on the basis of a
pressure change that is to be built up. The pumping capacity may be
increased, for example linearly, with the demanded pressure
change.
The noise level in the vehicle due to the pump may thus be kept
low, except in the case of a strong braking action in an
emergency.
One example embodiment of the method according to the present
invention determines a present dead volume of the brake system and
determines the pumping capacity as a function of the present dead
volume.
When the pump first starts up it may occur, depending on the design
of a brake circuit, that no braking action occurs at first. In
addition, the braking action may lag behind the expected braking
action of an intended setpoint pressure, or may not begin within a
required response time. The dead volumes in the brake circuits
first fill with brake fluid, without any pressure increase
occurring. The design provides for taking account of the dead
volumes in the brake circuits and increasing the pumping capacity
of the pump, preferably until the dead volumes are filled.
One brake system according to the present invention includes a pump
to build up a hydraulic pressure in a brake circuit to which at
least one brake element is connected, and a control system to set a
pumping capacity of the pump according to the example method
according to the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is explained below on the basis of preferred
specific embodiments and the figures.
FIG. 1 shows a block diagram of a brake system.
FIG. 2 shows a block diagram of the signal wiring of the brake
system.
FIG. 3 shows a flow chart for elucidating the method for operating
the brake system.
FIG. 4 shows a pressure-volume characteristic curve of the brake
system.
FIG. 5 shows an illustration of the pressure buildup during active
braking.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
FIG. 1 shows a schematic block diagram of a hydraulic brake system
10. Two mutually independent brake circuits are connected to a
brake master cylinder 12. In each of the brake circuits, a main
brake line 14 connects the brake master cylinder to two connected
wheel brakes 15, 16. Wheel brakes 15, 16, on one of the main brake
lines 14, may brake a front wheel and a diagonally opposite rear
wheel, as depicted in FIG. 1. Besides this so-called X brake
circuit split, however, any other division of the brake circuits is
also possible.
Main brake line 14 branches before wheel brakes 15, 16. Situated in
each of the branches is an inlet valve 18, which is open in a
normal position. A return line 19 leads away from each of the wheel
brakes 15, 16; these join in a common return line. Connected into
return lines 19 are outlet valves 20, which are closed in their
normal position.
A fluid reservoir 25 may be connected to one or both return lines
19. When wheel brakes 15, 16 are released, outlet valves 20 are
opened. The brake fluid may drain away into fluid reservoir 25,
whereby the hydraulic pressure acting on wheel brakes 15, 16 is
reduced. Brake master cylinder 12 is able to draw the brake fluid
from fluid reservoir 25 when outlet valve 20 and switchover valve
32 or a high pressure valve 30 are open. Otherwise the brake fluid
is transported back via pump elements 22, 23. The brake fluid is
thus available for another braking procedure.
Active braking or semi-active braking is made possible by
motor-driven pump elements 22, 23. In active braking, pressure is
built up in the brake circuits by pump elements 22, 23 alone.
During semi-active braking, pump elements 22, 23 support the
pressure buildup of operated master cylinder 12.
Pump element 22, 23 may be provided for each of the brake circuits.
An output side of pump element 22, 23 is connected to a line 33
between switchover valve 32 and inlet valve 18. Pump element 22, 23
is able to pump brake fluid into line 33, in order to increase the
pressure in line 33 and bring about a braking action of wheel
brakes 15, 16.
Brake master cylinder 12 may be connected via a high pressure valve
30 to the suction side of pump elements 22, 23. High pressure valve
30 is closed in its normal position.
A switchover valve 32 is integrated into main brake line 14.
Switchover valve 32 may connect the output side of pump element 22
to brake cylinder 12. In its normal position, switchover valve 32
is open. The flow of brake fluid through switchover valve 32 may be
halted by applying a control signal. Typically a threshold value is
set for a pressure difference between the inlet side and the outlet
side of switchover valve 32, above which switchover valve 32 opens.
The threshold value is set by the control signal.
A sensor 26 may be connected to main brake line 14, in order to
detect the pressure in main brake line 14. Additional pressure
sensors (not shown) may be integrated into wheel brakes 15, 16 or
situated in the direct supply lines to wheel brakes 15, 16.
Pump elements 22, 23 are driven by a shared motor 24. Inlet valves
18, outlet valves 20, switchover valves 32 and high pressure valves
30 may be designed as solenoid valves. A control system 40 is
connected to the valves in order to control inlet valves 18, outlet
valves 20, switchover valves 32 and high pressure valves 30. In
addition, control system 40 controls motor 24 for the pump
elements. Control system 40 conveys a control signal to set the
threshold value for switchover valve 32. The couplings of the
control system, valves 18, 20, 30, 32 and motor 24 to transmit
control signals are depicted in a block diagram in FIG. 2.
Rotational speed sensors may be connected to control system 40 in
order to detect slippage or blocking of the wheels. Control system
40 is able to open or close the valves accordingly, and activate
motor 24. The described brake system 10 makes standard braking,
braking intervention by a driver assistance system, anti-wheel-lock
control, driving slip, and/or vehicle dynamics control
possible.
The demands on the brake system are diverse. Interventions in the
driving behavior in moving traffic, for example in order to
maintain a constant distance from a preceding vehicle, should
proceed unnoticed by the driver. This requires exact metering of
the braking force. If skidding of the vehicle is to be prevented by
an active vehicle dynamics control system, rapid buildup and
reduction of the braking action on the wheels is required. Rapid
activation of the brake system requires a high pumping capacity of
pump elements 22, 23. However, increasing the pumping capacity is
also accompanied by increasing noise generation of pump elements
22, 23 and drive motor 24.
The specific embodiment described below controls drive motor 24 as
a function of a requested braking action. FIG. 3 shows the sequence
of the process as a flow chart.
In braking, a braking action is requested. The request may be
conveyed by operating a brake pedal, by a corresponding control
signal of a vehicle dynamics control system, a driver assistance
system (adaptive cruise control), etc., to control system 40
(S1).
The braking signal may specify to what extent the braking action is
to change. A measure of the appropriate pressure change in order to
set the braking action may be contained directly in the braking
signal. The braking signal may be a digital or an analog
signal.
Control system 40 determines a pumping capacity q on the basis of
the requested pressure change dp (S2). Pumping capacity q may be
increased linearly with requested pressure change dp according to
the following equation: q=Edp/dt.
A response time dt predefines the time span within which the
pressure change is to be built up. Response time dt may be firmly
specified by control system 40, for example as a maximum
permissible value. Response time dt may also be, for example, the
period in which the braking signals are transmitted.
In other embodiments, response time dt is specified by the braking
signal. A driver assistance system may ascertain, for example,
whether full braking is necessary, in which case an appropriately
short response time dt is chosen. In such a case, a high rate of
pressure change dp/dt is requested from pump system 22, 23, 24. On
the other hand, if the vehicle is supposed to maintain a constant
distance from the preceding vehicle in moving traffic, slow changes
of pressure dp in the brake system are sufficient; in that case the
braking signal may specify a high rate of change dt. Drive motor 24
of pump elements 22, 23 may be operated at low power, and the brake
system is correspondingly quiet.
Proportionality factor E is a value that is determined by the brake
circuit. FIG. 4 shows a function of pressure p in wheel brake 15,
16 on the volume V of brake fluid pumped into wheel brakes 15, 16.
Elasticity E may be defined as the quotients dV/dp around an
operating point plin. A corresponding measurement of the
pressure-volume characteristic of the brake circuit may be
performed during installation of brake system 10, and the
determined elasticity E is stored in control system 40.
In another embodiment it is provided to store the pressure-volume
characteristic in control system 40. Elasticity E for an
instantaneous actual pressure p0 is redetermined continuously from
the pressure-volume curve.
Control system 40 ascertains a rotational speed n for pump elements
22, 23, or for motor 24 which drives pump elements 22, 23 (S3) from
pumping capacity q. Rotational speed n may be determined according
to the following formula: n=q/(eV).
The efficiency e of pump elements 22, 23 and the pumped volume V
per pumping cycle of pump elements 22, 23 are taken into account.
If different rotational speeds n are ascertained for a plurality of
brake circuits of pump elements 22, 23 which are connected to the
same motor 24, the greatest of the ascertained rotational speeds n
is preferably selected.
The linear increase of pumping capacity q or of rotational speed n
may occur in a plurality of discrete steps, for example four or
more steps. Alternatively, pumping capacity q or rotational speed n
may be increased continuously.
Another specific embodiment refines the previous specific
embodiment. Dead volumes V0 are allowed for in the brake circuits
when determining pumping capacity q. When building up the pressure
by pumping in brake fluid, a dead volume V0 is filled first. Hence,
a pressure increase may not occur at the beginning of pumping, or
may lag behind the requested response time dt.
An example of a dead volume V0 may be air play caused by a gap
between the brake lining and the brake disk; under certain
circumstances the volume of the valves, main brake line 14, return
line 19, etc., may also contribute to the air play. Furthermore,
the volume of the brake circuit increases when brake pistons of
wheel brakes 15, 16 are pressed outward under the effect of the
hydraulic pressure, which also produces a non-linear behavior
between pressure p and volume V that may be attributed to dead
volume V0.
The dead volume V0 due to the air play may be ascertained for
various operating conditions of the brake system in sequences of
tests. The operating conditions include, for example, the operating
temperature and the transverse acceleration. The ascertained
tables, characteristics, etc., are stored in control system 40.
Control system 40 determines a pumping capacity q that is necessary
to fill dead volume V0 within a predefined time span T (S4).
Predefined time span T may be equal to response time dt. Pumping
capacity q is found according to: q=Edp/dt+V0/T.
Rotational speed n is determined as in the previous specific
embodiment, based on the pumping capacity q.
FIG. 5 shows the change of pressure p over time t for the described
specific embodiment. The rise of pressure p is supposed to be
increased over time t in accordance with dashed line 50, until
setpoint pressure P is reached. Pressure p may be increased
according to the time-dependent setpoint pressure, i.e., along
dashed line 50, if only a negligible dead volume V0 or none is
present in the brake circuit.
Pressure p builds up until a point in time T1, at which a setpoint
pressure P is reached. Continuous line 51 illustrates the behavior
when a dead volume V0 is present. No pressure increase occurs until
a point in time T2, because dead volume V0 is being filled.
Pressure p rises after that. Due to the increase in pumping
capacity q by V0/T, a dynamic in the pressure buildup is reached
that corresponds to a brake system without a dead volume V0.
Another specific embodiment takes dead volume V0 indirectly into
account. The pressure-volume characteristic according to FIG. 4 for
the brake circuit is stored in control system 40. The function may
be defined in the form of a table, a characteristic curve, or an
adapted polynomial.
Control system 40 receives the braking signal, in which the current
setpoint pressure to be attained is specified. The actual pressure
P0 in wheel brakes 15, 16 is determined using the pressure sensors,
or is estimated by control system 40 on the basis of a model. Based
on the stored pressure-volume function, the actual pressure P0, and
the current setpoint pressure to be attained, a volume V1 of brake
fluid is determined which, when pumped into line 33, raises the
instantaneous pressure from actual pressure P0 to the instantaneous
setpoint pressure. The pumping capacity q is determined as follows:
q=Edp/dt+V1/T.
Rotational speed n is determined as in the previous specific
embodiments, based on the pumping capacity q.
Another specific embodiment provides a setting reserve qr for high
dynamics when braking.
A transverse acceleration sensor detects acceleration values that
occur perpendicularly to the direction of travel (S5). Such
acceleration typically occurs due to the centrifugal force when
driving around a curve.
If the transverse acceleration exceeds a threshold value, pumping
capacity q is increased (S6). The increase qr may be proportional
to the detected transverse acceleration. The reason for the
additional pumping capacity qr is that if the transverse
acceleration increases further above a second threshold value, an
active vehicle dynamics control system is triggered and the vehicle
is stabilized by selective braking of the wheels. To ensure that
the vehicle dynamics control system continues to be triggered
quickly, pumping capacity q is increased by the amount of setting
reserve qr as a precaution.
In addition to the transverse acceleration, the vehicle speed,
distance from the vehicle ahead, recognition of a red light by an
image recognition system, etc., may contribute to an increase in
pumping capacity q.
The characteristic curves, in particular the pressure-volume
characteristic, are subject to fluctuations during operation. As a
result, the braking action may only be set or metered within a
tolerance range. In the case of one-time braking maneuvers or
short-term stabilizing braking maneuvers that monitor the braking
action through control loops, the fluctuations may be ignored. In
the case of steady braking or repeated braking in order to set a
defined speed of a vehicle or a defined distance from a preceding
vehicle, greater precision and greater repeat precision may be
required.
The specific embodiment described below utilizes switchover valves
32 in the brake circuit for this purpose. Using actuating signals,
switchover valves 32 may be set to a threshold value at which brake
fluid may drain from line 33 (S7). The switchover valves are used
to set a desired pressure in wheel brakes 15, 16 by setting the
threshold value to the desired pressure. Pumping capacity q is
intentionally kept at an excess increment qa above the minimum
necessary pumping capacity q, so that brake fluid is able to drain
away via switchover valves 32 when setpoint pressure P is reached
(S8). In FIG. 5 the effect of switchover valves 32 begins, for
example, at point in time T3. The threshold value of switchover
valves 32 is raised continuously until setpoint pressure P is
reached. This method makes it possible to reach setpoint pressure
P0 using a defined dynamic.
The repeat precision of switchover valves 32 may depend on the flow
through the switchover valve. The excess increment qa may therefore
preferably be chosen so that the switchover valve exhibits
sufficient repeat precision of the setpoint pressure at the excess
flow of brake fluid.
In one specific embodiment, all four contributions described above
are drawn upon to determine pumping capacity q:
q=Edp/dt+V1/T+qr+qa.
* * * * *